"Growth patterns in children with mucopolysaccharidosis type I-Hurler after hematopoietic stem cell transplantation: Comparison with untreated patients"

Persistent bone and joint disease despite current treatments for mucopolysaccharidosis types I, II, and VI: Data from a 10-year prospective study

The mucopolysaccharidosis (MPS) disorders have many potential new therapies on the horizon. Thus, historic control data on disease progression and variability are urgently needed. We conducted a 10-year prospective observational study of 55 children with MPS IH (N = 23), MPS IA (N = 10), non-neuronopathic MPS II (N = 13), and MPS VI (N = 9) to systematically evaluate bone and joint disease. Annual measurements included height, weight, and goniometry. Mixed effects modeling was used to evaluate changes over time. All participants had been treated with hematopoietic cell transplantation and/or enzyme replacement therapy. Height z-score decreased over time in MPS IH, MPS II, and MPS VI, but not MPS IA. Adult heights were 136 ± 10 cm in MPS IH, 161 ± 11 cm in MPS IA, 161 ± 14 cm in MPS II, and 128 ± 15 cm in MPS VI. Adult average BMI percentiles were high: 75 ± 30%ile in MPS IH, 71 ± 37%ile in MPS IA, 71 ± 25%ile in MPS II, and 60 ± 42%ile in MPS VI. Every participant had joint contractures of the shoulders, elbows, hips, and/or knees. Joint contractures remained stable over time. In conclusion, despite current treatments for MPS I, II, and VI, short stature and joint contractures persist. The elevation in average BMI may be related, in part, to physical inactivity due to the ongoing bone and joint disease. Data from this longitudinal historical control study may be used to expedite testing of experimental bone and joint directed therapies and to highlight the need for weight management as part of routine clinical care for patients with MPS.

MPSI Manifestations and Treatment Outcome: Skeletal Focus

Mucopolysaccharidosis type I (MPSI) (OMIM #252800) is an autosomal recessive disorder caused by pathogenic variants in the IDUA gene encoding for the lysosomal alpha-L-iduronidase enzyme. The deficiency of this enzyme causes systemic accumulation of glycosaminoglycans (GAGs). Although disease manifestations are typically not apparent at birth, they can present early in life, are progressive, and include a wide spectrum of phenotypic findings. Among these, the storage of GAGs within the lysosomes disrupts cell function and metabolism in the cartilage, thus impairing normal bone development and ossification. Skeletal manifestations of MPSI are often refractory to treatment and severely affect patients’ quality of life. This review discusses the pathological and molecular processes leading to impaired endochondral ossification in MPSI patients and the limitations of current therapeutic approaches. Understanding the underlying mechanisms responsible for the skeletal phenotype in MPSI patients is crucial, as it could lead to the development of new therapeutic strategies targeting the skeletal abnormalities of MPSI in the early stages of the disease.

Proposal of an Algorithm to Early Detect Attenuated Type I Mucopolysaccharidosis (MPS Ia) among Children with Growth Abnormalities

Background and Objectives: Diagnostic delay is common in attenuated Mucopolysaccharidosis Type I (MPS Ia) due to the rarity of the disease and the variability of clinical presentation. Short stature and impaired growth velocity are frequent findings in MPS Ia, but they rarely raise suspicion as paediatric endocrinologists are generally poorly trained to detect earlier and milder clinical signs of this condition. Materials and Methods: Following a consensus-based methodology, a multidisciplinary panel including paediatric endocrinologists, paediatricians with expertise in metabolic disorders, radiologists, and rheumatologists shared their experience on a possible clinical approach to the diagnosis of MPS Ia in children with short stature or stunted growth. Results: The result was the formation of an algorithm that illustrates how to raise the suspicion of MPS Ia in a patient older than 5 years with short stature and suggestive clinical signs. Conclusion: The proposed algorithm may represent a useful tool to improve the awareness of paediatric endocrinologists and reduce the diagnostic delay for patients with MPS Ia.